Showing papers on "Saturation (magnetic) published in 2017"

Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses

Abstract: Using a liquid phase epitaxy (LPE) technique (1 1 1) yttrium iron garnet (YIG) films with thicknesses of ≈100 nm and surface roughnesses as low as 0.3 nm have been grown on (1 1 1) gadolinium gallium garnet (GGG) substrates as a basic material for spin-wave propagation experiments in microstructured waveguides. The continuously strained films exhibit nearly perfect crystallinity without significant mosaicity and with effective lattice misfits of and below. The film/substrate interface is extremely sharp without broad interdiffusion layer formation. All LPE films exhibit a nearly bulk-like saturation magnetization of () Gs and an 'easy cone' anisotropy type with extremely small in-plane coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy with a pronounced six-fold symmetry observed for the saturation field <1.5 Oe. No significant out-of-plane anisotropy is observed, but a weak dependence of the effective magnetization on the lattice misfit is detected. The narrowest ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is the lowest value reported so far for YIG films of 100 nm thicknesses and below. The Gilbert damping coefficient for investigated LPE films is estimated to be close to .

Magnetic Materials Used in Electrical Machines: A Comparison and Selection Guide for Early Machine Design

Abstract: This article presents an up-to-date magnetic material investigation and overview on soft magnetic materials used in rotating electrical machines. The focus is on small-to-medium-sized high-performance and high-efficiency permanent-magnet and induction motors for different application scenarios. The investigated materials include fully processed silicon-iron (SiFe), nickel-iron (NiFe), and cobalt-iron (CoFe) lamination steels as well as soft magnetic composites (SMCs) and amorphous magnetic materials. This article focuses on the magnetic properties and iron losses as well as the manufacturing influence and required thermal treatments during the manufacturing process. A new loss-to-flux-density factor is introduced to compare the magnetization curve and the iron losses of different materials within the same diagram. This article provides a review and comparison of magnetic substances for use in high-performance machines.

Laminar and turbulent dynamos in chiral magnetohydrodynamics. II. Simulations

Abstract: Using direct numerical simulations (DNS), we study laminar and turbulent dynamos in chiral magnetohydrodynamics (MHD) with an extended set of equations that accounts for an additional contribution to the electric current due to the chiral magnetic effect (CME). This quantum phenomenon originates from an asymmetry between left- and right-handed relativistic fermions in the presence of a magnetic field and gives rise to a chiral dynamo. We show that the magnetic field evolution proceeds in three stages: (1) a small-scale chiral dynamo instability; (2) production of chiral magnetically driven turbulence and excitation of a large-scale dynamo instability due to a new chiral effect (alpha_mu effect); and (3) saturation of magnetic helicity and magnetic field growth controlled by a conservation law for the total chirality. The $\alpha_\mu$ effect becomes dominant at large fluid and magnetic Reynolds numbers and is not related to kinetic helicity. The growth rate of the large-scale magnetic field and its characteristic scale measured in the numerical simulations agree well with theoretical predictions based on mean-field theory. The previously discussed two-stage chiral magnetic scenario did not include stage (2) during which the characteristic scale of magnetic field variations can increase by many orders of magnitude. Based on the findings from numerical simulations, the relevance of the CME and the chiral effects revealed in the relativistic plasma of the early universe and of proto-neutron stars are discussed.

Low-Field-Triggered Large Magnetostriction in Iron-Palladium Strain Glass Alloys

Abstract: Development of miniaturized magnetostriction-associated devices requires low-field-triggered large magnetostriction. In this study, we acquired a large magnetostriction (800 ppm) triggered by a low saturation field (0.8 kOe) in iron-palladium (Fe-Pd) alloys. Magnetostriction enhancement jumping from 340 to 800 ppm was obtained with a slight increase in Pd concentration from 31.3 to 32.3 at. %. Further analysis showed that such a slight increase led to suppression of the long-range ordered martensitic phase and resulted in a frozen short-range ordered strain glass state. This strain glass state possessed a two-phase nanostructure with nanosized frozen strain domains embedded in the austenite matrix, which was responsible for the unique magnetostriction behavior. Our study provides a way to design novel magnetostrictive materials with low-field-triggered large magnetostriction.

Soft Magnetic Properties of Magnetic Cores Assembled With a High B_{s} Fe-Based Nanocrystalline Alloy

Abstract: Soft magnetic properties of magnetic cores assembled with Fe 81.8 Cu 1.0 Mo 0.2 Si 4 B 14 nanocrystalline alloy ribbon are discussed. The nanocrystalline alloy ribbon was cast in an amorphous phase by a melt quenching method, and a nanocrystalline phase was obtained by high-heating rate annealing. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon exhibits magnetic flux density B 800 at 800 A/m of 1.74 T, core loss P 16/50 at 50 Hz, and at 1.5 T of 0.29 W/kg. A racetrack-shaped core, which includes curved and straight sections in the same core, exhibits core losses at 1.0 T and at 400 Hz and 1 kHz of 1.5 and 5 W/kg, respectively. These core losses are as low as those of Fe-based amorphous alloys. A medium-size toroidal core assembled with this nanocrystalline alloy ribbon, secondarily annealed under a perpendicular magnetic field, exhibits core loss P 2/10k at 0.2 T and at 10 kHz of 2 W/kg. This value of core loss is one of the lowest values for the metallic magnetic cores, which have a saturation induction B s higher than 1.5 T. A core assembled with this material can be used in several applications from low to medium frequency ranges. Since this material exhibits a higher B s and one half of the saturation magnetostriction λ s of Fe-based amorphous alloys with comparable core losses, the most possible applications are in such applications as distribution transformers and inductors in power electronics.

The effect of Y3+ substitution on the structural, optical band-gap, and magnetic properties of cobalt ferrite nanoparticles.

Abstract: In this study we investigated the structural, optical band-gap, and magnetic properties of CoYxFe2−xO4 (0 ≤ x ≤ 004) nanoparticles (NPs) synthesized using a combustion reaction method without the need for subsequent heat treatment or the calcing process The particle size measured from X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images confirms the nanostructural character in the range of 16–36 nm The optical band-gap (Eg) values increase with the Y3+ ion (x) concentration being 330 and 358 eV for x = 0 and x = 004, respectively The presence of yttrium in the cobalt ferrite (Y-doped cobalt ferrite) structure affects the magnetic properties For instance, the saturation magnetization, Ms and remanent magnetization, Mr, decrease from 69 emu g−1 to 33 and 28 to 12 emu g−1 for x = 0 and x = 004, respectively On the other hand the coercivity, Hc, increases from 1100 to 1900 Oe for x = 0 and x = 004 at room temperature Also we found that Ms, Mr, and Hc decreased with increasing temperature up to 773 K The cubic magnetocrystalline constant, K1, determined by using the “law of approach” (LA) to saturation decreases with Y3+ ion concentration and temperature K1 values for x = 0 (x = 004) were 33 × 106 erg cm−3 (20 × 106 erg cm−3) and 04 × 106 erg cm−3 (03 × 106 erg cm−3) at 300 K and 773 K, respectively The results were discussed in terms of inter-particle interactions induced by thermal fluctuations, and Co2+ ion distribution over tetrahedral A-sites and octahedral B-sites of the spinel structure due to Y3+ ion substitution

Synthesis and characterization of yttrium iron garnet (YIG) nanoparticles - Microwave material

Abstract: Magnetic Yttrium Iron Garnet (YIG) nanoparticles (NPs) were prepared by sol–gel (SG) and solid-state (SS) reaction methods to elucidate the nanoscale size on the magnetic behavior of NPs. It is found that YIG prepared by these two methods are different in many ways. The average NP sizes prepared by SG and SS methods were calculated by Scherrer formula from XRD data. SEM images show the change in grain size for both types of NPs. The sintering temperature required to form pure garnet phase is 750°C for SG and 1000°C for SS NPs. The saturation magnetizations (Ms) were 1070 Oe for SG and 1125 Oe for SS NPs, respectively. The coercivity (Hc) of SS NPs are twice larger than SG NPs. This is due to the larger crystal sizes of the SS NPs, hence more crystal boundaries. Dynamic properties were studied by ferromagnetic resonance (FMR) technique in field-sweep and frequency-sweep mode at different fixed frequencies and at different fixed magnetic fields, respectively. Resonance field (Hr) observed to increase linear...

Effects of Short-Range Order on the Magnetic and Mechanical Properties of FeCoNi(AlSi)x High Entropy Alloys

Abstract: The properties of a material are sensitive to chemically-ordered structure in multi-element alloys. Understanding the effects of chemical short-range order (SRO) on magnetic and mechanical properties is important. In this work, we use the Monte Carlo method in combination with density functional theory to investigate atomic nearest neighbor distribution, magnetic moment and elastic modulus in FeCoNi (AlSi)x alloys. It is found that the prominent feature of the FeCoNi (AlSi)x alloys is the change of SRO parameters: the SRO parameters are positive between Al-Al, Al-Si, Si-Si pairs and negative between Ni-Al, Co-Si, Fe-Co, Ni-Si and Fe-Si pairs. The Al and Si elements tend to bond with Fe, Co, Ni elements to form an SRO structure. The change of the atomic nearest neighbor environment leads to a reduction in the atomic magnetic moments of magnetic elements. The calculated saturation magnetizations by considering the effect of SRO are in good accord with the experimental values. We further show that SRO leads to an increase of the elastic modulus, by sacrificing ductility and isotropy. In the study of the structure and properties of high entropy alloys, the effect of SRO should not be ignored.

Comparison of Axial Flux Permanent Magnet Synchronous Machines With Electrical Steel Core and Soft Magnetic Composite Core

Abstract: This paper presents a comparison of axial flux permanent magnet machines (AFPMs) with an electrical steel core and that with a soft magnetic composite (SMC) core SMCs have several advantages such as low core loss and low eddy current loss However, compared with electrical steel, SMCs have poor magnetic properties such as low flux density saturation and unsaturated relative permeability The analysis of the electromagnetic characteristics in a wide frequency range revealed that for an AFPM using an electric steel core, the performance was excellent in a low-frequency range; however, for an AFPM using an SMC core, the performance improves with an increase in frequency Finally, the operation area of an AFPM using an SMC core is proposed

A small-scale dynamo in feedback-dominated galaxies – II. The saturation phase and the final magnetic configuration

Abstract: Magnetic fields in galaxies are believed to be the result of dynamo amplification of initially weak seed fields, reaching equipartition strength inside the interstellar medium. The small-scale dynamo appears to be a viable mechanism to explain observations of strong magnetic fields in present-day and high-redshift galaxies, considering the extreme weakness of seed fields predicted by battery mechanisms or primordial fields. Performing high-resolution adaptive mesh magneto-hydrodynamic simulations of a small mass, isolated cooling halo with an initial magnetic seed field strength well below equipartition, we follow the small-scale dynamo amplification from supernova-induced turbulence up to saturation of the field. We find that saturation occurs when the average magnetic pressure reaches only 3 % to 5 % of the turbulent pressure. The magnetic energy growth transitions from exponential to linear, and finally comes to halt. The saturation level increases slightly with grid resolution. These results are in good agreement with theoretical predictions for magnetic Prandtl numbers of order $\mathrm{Pr_M} \sim 1$ and turbulent Mach numbers of order $\mathrm{M} \sim 10$. When we suppress supernova feedback after our simulation has reached saturation, we find that turbulence decays and that the gas falls back onto a thin disk with the magnetic field in local equipartition. We propose a scenario in which galactic magnetic fields are amplified from weak seed fields in the early stages of the Universe to sub-equipartition fields, owing to the turbulent environment of feedback-dominated galaxies at high redshift, and are evolved further in a later stage up to equipartition, as galaxies transformed into more quiescent, large spiral disks.

Three-dimensional supercritical resolved light-induced magnetic holography

Abstract: In the era of big data, there exists a growing gap between data generated and storage capacity using two-dimensional (2D) magnetic storage technologies (for example, hard disk drives), because they have reached their performance saturation. 3D volumetric all-optical magnetic holography is emerging rapidly as a promising road map to realizing high-density capacity for its fast magnetization control and subwavelength magnetization volume. However, most of the reported light-induced magnetization confronts the problems of impurely longitudinal magnetization, diffraction-limited spot, and uncontrollable magnetization reversal. To overcome these challenges, we propose a novel 3D light-induced magnetic holography based on the conceptual supercritical design with multibeam combination in the 4π microscopic system. We theoretically demonstrate a 3D deep super-resolved ( ∼ λ 3 59 ) purely longitudinal magnetization spot by focusing six coherent circularly polarized beams with two opposing high numerical aperture objectives, which allows 3D magnetic holography with a volumetric storage density of up to 1872 terabit per cubic inches. The number and locations of the super-resolved magnetization spots are controllable, and thus, desired magnetization arrays in 3D volume can be produced with properly designed phase filters. Moreover, flexible magnetization reversals are also demonstrated in multifocal arrays by using different illuminations with opposite light helicity. In addition to data storage, this magnetic holography may find applications in information security, such as identity verification for a credit card with magnetic stripe.

Controlling orientational order in block copolymers using low-intensity magnetic fields

Abstract: The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP's anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields ( 4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system's nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles.

Numerical Simulation and Experimental Validation of the Critical Pressure Value in Ferromagnetic Fluid Seals

Abstract: Ferrofluids have various engineering applications, and one of them is magnetic fluid seals. Development for this design is a complex process, which requires knowledge about ferrofluid physical properties and magnetic field distribution inside the sealing gap. One of the most important parameters of ferromagnetic fluid seals is a critical pressure value. It is a pressure at which rapid leakage will occur. This publication presents the results of critical pressure value obtained from experimental studies and calculations based on numerical simulations. Shape of sealing stage, volume of ferrofluid, and volume of permanent magnet used in seal construction were taken into account. Experiments and calculations were performed for four ferrofluids differ in saturation magnetization, density, and zero magnetic field viscosity.

Magnetic and photocatalytic studies on Zn1 −xMgxFe2O4 nanocolloids synthesized by solvothermal reflux method

Abstract: Biocompatible magnetic semiconductor Zn1-xMgxFe2O4 (x=0, 0.1, 0.3, 0.5 & 0.7) nanoparticles of around 10nm diameter were synthesized by solvothermal reflux method. The method produces well separated and narrow size distributed nanoparticles. Crystal structure, morphology, particles surface properties, surfactant quantity, colloidal stability, magnetic properties and photocatalytic properties of the synthesized nanoparticles were studied. Different characterizations confirmed that all compounds were single crystals and superparamagnetic at room temperature. Saturation mass magnetization (Ms=57.5emu/g) enhances with substituent Mg2+ concentration due to promotion of mixed spinel (normal and inverse) structure. Photocatalytic activity of all synthesized magnetic semiconductor nanoparticles were studied through methylene blue degradation. The degradation of 98% methylene blue was observed on 60 min irradiation of light. It is observed that photocatalytic activity slightly enhances with substituent Mg2+ concentration. The synthesized biocompatible magnetic semiconductor nanoparticles can be utilized as photocatalysts and could also be recycled and separated by applying an external magnetic field.